Epstein-Barr virus (EBV or HHV4), a member of the human herpesvirus (HHV) family, has recently been shown to encode microRNAs (miRNAs). In contrast to most eukaryotic miRNAs, these viral miRNAs do not have close homologs in other viral genomes or in the genome of the human host. To identify other miRNA genes in pathogenic viruses, we combined a new miRNA gene prediction method with small-RNA cloning from several virus-infected cell types. We cloned ten miRNAs in the Kaposi sarcoma-associated virus (KSHV or HHV8), nine miRNAs in the mouse gammaherpesvirus 68 (MHV68) and nine miRNAs in the human cytomegalovirus (HCMV or HHV5). These miRNA genes are expressed individually or in clusters from either polymerase (pol) II or pol III promoters, and share no substantial sequence homology with one another or with the known human miRNAs. Generally, we predicted miRNAs in several large DNA viruses, and we could neither predict nor experimentally identify miRNAs in the genomes of small RNA viruses or retroviruses.

IgG2a is known to be the most efficient antibody isotype for viral clearance. Here, we demonstrate a unique pathway of B-cell activation, leading to IgG2a production, and involving synergistic stimulation via B-cell antigen receptors, toll-like receptor 7 (TLR7), and IFNγ receptors on B cells. This synergistic stimulation leads to induction of T-box transcription factor T-bet expression in B cells, which, in turn, drives expression of CD11b and CD11c on B cells. Tbet/CD11b/CD11c positive B cells appear during antiviral responses and produce high titers of antiviral IgG2a antibodies that are critical for efficient viral clearance. The results thus demonstrate a previously unknown role for T-bet expression in B cells during viral infections. Moreover, the appearance of T-bet + B cells during antiviral responses and during autoimmunity suggests a possible link between these two processes.interferon gamma | virus

Murine gammaherpesvirus 68 (␥HV68; also referred to as MHV68) infection of mice is a developing small-animal model for analysis of gammaherpesvirus pathogenesis (reviewed in references 18, 19, 45, 46, 64, and 69). ␥HV68 is a gamma-2 herpesvirus which is closely related to the human and primate gammaherpesviruses Epstein-Barr virus (EBV), Kaposi's sarcoma-associated herpesvirus (KSHV), and herpesvirus saimiri (HVS) (22,67). Acute ␥HV68 infection of laboratory mice is cleared by 2 to 3 weeks postinfection, with the concomitant establishment of a presumably life-long latent infection. Notably, several ␥HV68 genes that are also present in HVS, KSHV, and/or EBV have been identified as candidate latent genes by transcriptional analysis of latently infected mice (68). These genes include those encoding the viral bcl-2 (v-bcl2) homolog and the viral G-protein-coupled receptor (v-GPCR) homolog as well as gene 73, which in KSHV encodes the latency-associated nuclear antigen (LANA) (11,35,50). In addition, KSHV, HVS, and ␥HV68 have in common a complement-regulatory protein homolog (1, 2, 26, 33, 67), and in both HVS and ␥HV68 this protein occurs in membrane-bound and soluble isoforms (26,33). These studies argue strongly that ␥HV68 shares mechanisms of pathogenesis with other gammaherpesviruses.Manipulation of the host cell cycle is a shared feature of gammaherpesviruses, and one focus for this regulation is the D-type cyclins. EBV infection (or expression of the EBV latency-associated membrane protein 1) upregulates expression of host cyclin D2 (3, 9, 63). In contrast, the gamma-2 herpesviruses HVS (32, 47), KSHV (2, 47, 52), and ␥HV68 (67) all contain open reading frames (ORFs) predicted to encode homologs of mammalian D-type cyclins. The viral cyclins (v-cyclins) exhibit 25 to 31% identity to mammalian D-type cyclins and 26 to 32% identity to each other, and they are positionally conserved in the gamma-2 herpesvirus genomes (67). Notably, the highest level of sequence conservation among these homologs is within the cyclin box, a domain demonstrated to be essential for cyclin-dependent kinase (cdk) binding (29,31,37,38,43,51).The biochemistry of the KSHV and HVS proteins has been intensively studied. The KSHV and HVS v-cyclins, in conjunction with cdk's, have been demonstrated to phosphorylate the retinoblastoma protein (pRb) and promote cell cycle progression, like their mammalian homologs (2, 8). The KSHV and HVS v-cyclins predominantly bind cdk6. Overexpression of the KSHV v-cyclin in cells expressing high levels of cdk6 results in apoptosis (48), suggesting that there may be other viral genes responsible for preventing apoptosis (e.g., v-bcl2). Several unusual properties of the v-cyclins have also been noted. The v-cyclin ORFs lack an LXCXE motif present in mammalian cyclin D proteins and thought to be important in direct binding to pRb (20,25). The HVS and KSHV v-cyclins are able to bind multiple cdk's, rather than being restricted to binding cdk4 and cdk6 (27,32,39), and have a broadened substrate range, being capa...